In the past oil coolers have included a plurality of plates joined together to form a heat exchanger adapted to be connected in a coolant space of a radiator (or other suitable heat sink) for extracting heat from oil in a transmission or other apparatus in which the oil is circulated and heated during the operation of the transmission or other apparatus.
Oil cooler centers are located in the oil passages within such oil coolers to mix the oil so as to improve heat transfer therefrom. One such center is a strip fin of high heat conductivity metal such as copper which is inserted between two plates forming the walls of a longitudinally directed oil flow path through which oil is directed for extracting heat therefrom. In such arrangements the strip fins have included louvers in the walls of the strip fin arranged to extend along the height of the fin wall and wherein the mixing is limited to the plane of the oil flow through the oil passages within the oil cooler, e.g., the louvers only mixed the oil flow from side to side of the oil passage rather than up and down within the oil passage.
One problem with such arrangements is that the oil mixing pattern is in a direction which does not act of thermal boundary areas at the inner surface of the plates comprising the oil flow passages through the oil cooler.
Other prior art oil coolers are known in which a metal insert of high heat conductivity is inserted between oil cooler plates. Such prior art arrangements however, do not include sinusoidally configured oil centers which can be easily roll formed to a final shape that will fit existing oil cooler having the old stype strip fin centers. Examples of such prior art oil coolers include U.S. Pat. No. 2,222,721 having a corrugated plate therein with openings formed by webs in the plate to direct oil between spaced plates and U.S. Pat. No. 2,990,163 in which a corrugated strip is located in both cases oil is mixed side to side of the oil flow rather than up and down in the oil flow passage. U.S. Pat. No. 4,373,578 discloses a cylindrically shaped oil cooler in which a generally star shaped insert is located on the water side to mix the water to improve heat transfer from an annular oil passage that does not have an oil mixing insert therein. U.S. Pat. No. 4,580,625 shows an oil cooler with sinusoidal fins for oil cooling. The prior art configurations do not disclose an easily fabricated oil center for mixing oil while breaking up the thermal boundary layer in the oil flow therethrough